The present invention relates to expandable intraluminal vascular grafts, generally referred to as stents. More precisely, the present invention is directed to a stent constructed from stainless steel that is virtually free of any traces of nickel and can have a metallic cladding.
Stents are used to maintain patency of vessels in the body. A variety of delivery systems have been devised that facilitate the placement and deployment of stents. The stent is initially manipulated while in its contracted or unexpanded state, wherein its reduced diameter more readily allows it to be introduced into the body lumen and maneuvered into the target site where a lesion has been dilated. Once at the target site, the stent is expanded into the vessel wall to allow fluid to more freely flow through the stent, thus performing a scaffolding function. Such stents usually are mounted on balloon catheters and are expanded by inflating the balloon on which the stent is mounted. Deflation of the balloon and removal of the catheter leave the stent implanted in the vessel in an expanded state.
Stents are typically formed from biocompatible metals such as stainless steel, nickel-titanium, tantalum, and the like, which provide sufficient hoop strength to perform the scaffolding function. Furthermore, stents have minimal wall thicknesses in order to minimize blood flow blockage. However, stents can sometimes cause complications including thrombosis and neointimal hyperplasia, such as by inducement of smooth muscle cell proliferation at the site of implantation of the stent. Such stents typically also do not provide for delivery of localized therapeutic pharmacological treatment of a blood vessel at the location being treated with the stent, which can be useful for overcoming such problems.
In the evolution of stents, there have been developments in the field of stents coated with a layer of polymers. The polymeric materials are typically capable of absorbing and releasing therapeutic drugs. Examples of such stents are disclosed in U.S. Pat. No. 5,443,358 to Eury; U.S. Pat. No. 5,632,840 to Campbell; U.S. Pat. No. 5,843,172 to Yan; and U.S. Ser. No. 08/837,993, filed Apr. 15, 1997, by Yan.
Aside from coated stents, there have been developments in the field of multilayer grafts. An example of a multilayer graft is disclosed in U.S. Pat. No. 4,743,252 to Martin, Jr. et al. Martin et al. shows a composite graft having a porous wall structure to permit ingrowth, which graft includes a generally non-porous, polymeric membrane in the wall to prevent substantial fluid passage therethrough so as to provide an implantable porous graft that does not require preclotting prior to implantation.
Grafts sometimes have multiple layers for strength reinforcement. For example, U.S. Pat. No. 5,282,860 to Matsuno et al. discloses a stent tube comprising an inner tube and an outer polyethylene tube with a reinforcing braided member fitted between the inner tube and the outer tube. The inner tube is made of a fluorine-based resin.
U.S. Pat. No. 5,084,065 to Weldon et al. discloses a reinforced graft assembly made from a vascular graft component and a reinforcing sleeve component. The reinforcing sleeve component may include one or more layers. The second component of the two component system includes the reinforcing sleeve component. Like the graft component, the reinforcing component includes a porous surface and a porous subsurface. Specifically, the reinforcing sleeve component includes multiple layers formed from synthetic, biologic, or biosynthetic and generally biocompatible materials. These materials are typically biocompatible polyurethane or similar polymers.
Notably, it has been observed that some prior art stents implanted in a body lumen have been prone to corrosion over time. This corrosion can reduce the yield strength of the stent and produce a danger to the patient. Therefore, it would be desirable to produce a stent that has a relatively high resistance to corrosion over the life of the patient.
What has been needed and heretofore unavailable is a substantially nickel-free stent that possesses improved elongation and mechanical properties, including resistance to corrosion. It is also desirable that such a stent have relatively good ductility, yet maintain a high yield strength. The present invention satisfies these and other needs.
The present invention is directed to an expandable intraluminal vascular graft, generally referred to as a stent. More precisely, the present invention is directed to a stent constructed from stainless steel that is virtually free of any traces of nickel and has a metallic cladding.
In one aspect of the invention, there is provided a stent constructed from stainless steel that is virtually free of any trace of nickel. xe2x80x9cNickel-freexe2x80x9d stainless steel has some particular advantages over 316L stainless steel which is a widely used material for manufacturing stents, particularly coronary stents. These advantages include the virtual elimination of nickel which can otherwise cause allergic reactions in some patients when implanted in an artery. Nickel-free stainless steel also can have greater strength and ductility as compared to 316L stainless steel.
In another aspect of the present invention, there is provided a substrate tube having an exterior, wherein the substrate tube is formed from stainless steel that is virtually free of any trace of nickel. A metallic cladding can be mechanically interlocked under pressure over the exterior of the substrate tube. The metallic cladding can include a radiopaque material. A pattern of stent struts can then be formed in the substrate and metallic cladding.
In another aspect, a pattern of stent struts are interconnected to form a structure that contacts a body lumen wall to maintain the patency of the body lumen. The structure includes a substrate made from nickel-titanium, a first metallic cladding made from a stainless steel that is virtually free of any trace of nickel, and a second metallic cladding made from a radiopaque material.
In another aspect of the invention, there is a first cladding mechanically interlocked under pressure over the exterior of the substrate tube. This first cladding can be formed from a radiopaque material. A second cladding then can be mechanically interlocked under pressure over the exterior of the first cladding. The second cladding can be formed from stainless steel that can be virtually free of any trace of nickel. A pattern of stent struts can be formed in the substrate and metallic claddings.
The present invention is also directed to a method of fabricating a stent for implantation within a body lumen including the step of providing a substrate tube having an outside surface and an inside surface, wherein the substrate tube is formed from stainless steel that is virtually free of any trace of nickel. A first cladding tube is disposed over the substrate tube, wherein the first cladding tube includes a radiopaque material selected from the group of radiopaque materials including platinum-10% iridium, platinum, gold, palladium, tantalum, tungsten, and other radiopaque materials. The first cladding tube is joined to the outside surface of the substrate tube to form a laminated tube. Stent struts are then formed in the laminated tube by selectively removing portions of the laminated tube to form a strut pattern.
In another aspect of the invention, a method of fabricating a stent for implantation within a body lumen includes the step of providing a substrate tube having an outside diameter, wherein the substrate tube is formed from stainless steel that is virtually free of any trace of nickel. A first cladding tube is provided having an inside diameter which has an interference fit with the outside diameter of the substrate tube. The first cladding tube may be a radiopaque material selected from a group of radiopaque materials including platinum-10% iridium, platinum, gold, palladium, tantalum, tungsten, and other radiopaque materials. The first cladding tube is disposed over the substrate tube and is joined to the substrate tube to form a laminated tube. A pattern of stent struts are then formed in the laminated tube to create the stent.
The present invention also is directed to a method of fabricating a stent for implantation within a body lumen including the step of providing a substrate sheet having an outside surface and an inside surface, wherein the substrate sheet is formed from stainless steel that is virtually free of any trace of nickel. A first cladding sheet is disposed over the substrate sheet and is joined to the outside surface of the substrate sheet to form a laminated sheet. The first cladding sheet may include a radiopaque material selected from a group of radiopaque materials including platinum-10% iridium, platinum, gold, palladium, tantalum, tungsten, and other radiopaque materials. The laminated sheet is then rolled into a laminated tube. The laminated tube is welded and stent struts are formed in the laminated tube. As a result, the finished stent has a cladding layer laminated onto the nickel-free tubular substrate.
Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings.